The field of this invention relates to manually operated devices to assist in the lifting of heavy objects.
A lift is basically a device for achieving vertical transportation (against gravity) of a heavy device which cannot be easily manually lifted. Typical heavy devices are automobile engines, motors, pumps, generators, etc.
In the manufacturing and servicing of such heavy equipment, it is necessary to move such equipment a spaced distance above the floor of the building in which servicing or manufacturing would be occurring. Because of the inherent weight of such structures, it is necessary to employ some type of lifting device in which a high mechanical advantage is obtained, so that when operated, the heavy equipment is thereby raised.
A common type of device would be a platform which operates either through a gearing mechanism or a screw mechanism to achieve raising of the platform with respect to a fixed frame. Such lifting devices in the past have been quite common. The lifting action is obtained through the use of a crank which is manually rotated through an input shaft to cause rotation of the screw or gears to obtain the lifting of the platform upon which has been located the piece of heavy equipment.
Normally, such lifting devices include the use of a locking pawl to lock the crank arm in position when a described lifted height has been obtained. At times it has been an infrequent occurrence that the locking pawl does not engage properly or accidentally becomes disengaged and, as the crank arm is released, it quickly spins in the reverse direction. If during this reverse rotation of the crank arm, it happens to come into contact with the operators arm, substantial injury can occur with a broken arm being the most common occurrence.